Qiangduo Tibetan Paper (Yunnan, China): Intrinsic Correlations Among Surface Properties, Absorption Performance, Dry Heat Durability, and Its Cultural Heritage Conservation Value

Qiangduo Tibetan paper is a typical intangible cultural heritage in the Shangri-La region of Yunnan, China, mainly handmade from two local fibrous plants, Stellera chamaejasme and Wikstroemia canescens. This study focuses on the correlations among its surface properties, water absorption and dry heat durability, which are critical for heritage conservation. Four paper samples (Z1–Z4) were investigated via micromorphology, physicochemical property testing and dry heat aging (105 °C, 216 h). The results show that the two raw materials lead to distinct fiber and pore structures: Stellera chamaejasme paper has coarser fibers and loose pores, while Wikstroemia canescens paper has finer and denser fibers. All samples present a near-neutral to weakly alkaline pH (6.87–7.56) and favorable water absorption, jointly regulated by fiber structure and alkaline wood ash fillers. After dry heat aging, all samples undergo whiteness loss, tensile index decay and slight acidification, with extremely significant changes (p < 0.001). Notably, Stellera chamaejasme paper exhibits much higher aging resistance, with whiteness and tensile index retention reaching 77.97%–93.07% and 71.46%–74.77% respectively, far superior to Wikstroemia canescens paper. The mechanism lies in the high flavonoid content and low lignin level in Stellera chamaejasme fibers, which enhance antioxidant stability and reduce yellowing, whereas the opposite composition accelerates degradation in Wikstroemia canescens paper. This study provides a scientific basis for the conservation, inheritance and targeted application of Qiangduo Tibetan paper, supports the sustainable protection of handmade paper cultural relics, and enriches the application of surface science in cultural heritage conservation.